Internal actuator for impacting a serial printer print head

ABSTRACT

A novel internal actuator for impacting the print head of a high speed serial printer with a print medium is disclosed. The internal actuator engages the interior of a rotatably and axially positionable print head and causes the latter to impact the print medium. The internal actuator includes a pivotal yoke portion and a neck portion, the latter of which extends into the interior of the print head. The pivotal yoke portion provides a fixed point about which the print head moves while the neck portion provides a firm mounting for both the positioned print head and the positioning shaft structure which is contained therein.

[111 3,739,897 [451 June 19,1973

United States Patent 1 Pateuk et a1.

INTERNAL ACTUATOR FOR IMPACTING A SERIAL PRINTER PRINT HEAD 3,608,692 9/1971 Henry 3,291,041 12/1966 Burchfield et a1. 1,652,463 12/1927 Tyberg.................. 3,406,807 10/1968 Sasaki 3,605,978 9/1971 Kawano 2,080,966 5/1937 Gliffilh Primary Examiner-Edgar S. Burr Honeywell Information Systems AttorneyR0nald T. Reiling and Fred Jacob w 3. M m W e n g H S .A H 7 [221 Filed:

[57] ABSTRACT A novel internal actuator for impacting the print head Dec. 1, 1970 [211 Appl. No.: 94,034

of a high speed serial printer with a print medium is disclosed. The internal actuator engages the interior of a rotatably and axially positionable print head and causes the latter to impact the print medium. The internal actuator includes a pivotal yoke portion and a neck por-' 42., BB 001 7. Q in 4 W w .M m7 w 9 l 1 5 n 5 u l a 7 9 u .l m u mu mm Wa L M Q e UlF .11] 2 8 555 [11.

tion, the latter of which extends into the interior of the print head. The pivotal yoke portion provides a fixed point about which the print head moves while the neck [56] References Cited UNITED STATES PATENTS portion provides a firm mounting for both the positioned print head and the'positioning shaft structure which is contained therein.

12 Claims, 6 Drawing Figures Beattie et mm mm .mw ea TK 66 0 6377 9999 1111 4628 110115 4594 1 7436 4499 1 2 3233 Waldenburger PATENIEU Jun '1 9 I975 summ HAROLD M. SHNEIDER STEVEN P. CAHILL .JAMES G. BATH Attorney PAIENIEU JUN I 91915 same nr's lNVENTORS 86 CONSTANTINEJPATEUK HAROLD M. SHNEIDER STEVEN F? CAHILL JAMES G. BATH Attorney PATENTEUJBM 9191s sum-Jar 3 lNVENTORS CONSTANTINE J. PATEUK HAROLD M. SHNEIDER STEVEN F! CAHILL JAMES G. BATH Attorney INTERNAL ACTUATOR FOR IMPACTING A SERIAL PRINTER PRINT HEAD BACKGROUND OF THE INVENTION The present invention relates to improvements in high speed impact printers, and more particularly, to the rotatable and axially displaceable type of print head assembly used in serial printers.

The serial printer concept may be stated quite simply as the rotational and axial displacement of a print head to position a given character on the print head surface. The print head surface contains a number of bands with each band itself containing a number of distinct characters. To position a particular character, the printer head must be moved to a particular band and then subsequently rotated to a given character within the selected band. Printing of the positioned character is then accomplished by singularly impacting it with a suitable print medium.

The serial printer concept has particular application in a small computer system wherein speed can be somewhat sacrificed in return for a significant saving in cost. This cost saving can be appreciated when the serial printer is compared to the typical high speed printer utilized in todays large computer systems. The high speed printer used most often in large systems today is the parallel printer wherein a series of parallel impacting means are provided for a plurality of parallel bands of rotatably positionable characters located on a drum surface. This arrangement of providing a number of parallel impacting means allows for the printing of a character without having to move the character drum to a particular band position. The resulting one less movement makes the parallel printer much faster than the serial printer, but at a substantial cost due to the large number of parallel impacting means that are re quired.

While the serial printer represents a significant saving in cost over the parallel printer, it must nonetheless still be fairly quick and accurate. This means that the various motions of the serial printer print head must be implemented in such a manner to achieve both a relatively high positioning speed as well as a high quality of print out. Two distinct types of print movement are thus necessary: (1) a given character on the print head surface must first by positioned and (2) the positioned character must be thereafter impacted with the print medium.

The positioning of a given character on the print head surface has previously been implemented by numerous mechanical drives including various combinations of gears, belts and pulleys. This has resulted in positioning systems marked by slowness and inaccuracy due to built-in flexibilities, mechanical deadspaces and inertial loadings. Various impacting devices have also been devised, some of which have been necessarily complex to accommodate the positioning apparatus. One approach to impact printing has been to pivot an entire carriage structure containing both the print head and the associated positioning apparatus. This results in a system with a high amount of inertia in the impacting apparatus. Another approach has been to mount the print head atop a flexible rod and impact the print head by an external hammer source. This results in a print head stroke which is dependent on where and how the shaft itself is flexed which is neither fixed nor definite. Yet another approach has been to employ a separate impact hammer arrangement which drives the print medium toward the positioned character. This system requires the synchronous lateral movement of a separate impacting device that moves in conjunction with a print head on the opposite side of the print medium.

The present invention, therefore, has an object to provide a serial printer with an impacting printhead apparatus which is quick and accurate possessing a minimal amount of inertial influence.

Another object of this invention is to provide a serial printer with a fixed and predetermined travel during the impacting stroke.

Yet another object of this invention is to provide a serial printer with a rigid internal actuation within the print head itself to accomplish the impacting stroke.

A still further object of this invention is to provide a serial printer with a combined structure that both positions and impacts a particular character, the structure being located within the print head shell itself and directly behind the character which is to be positioned.

SUMMARY OF THE INVENTION To achieve the above-mentioned objects, the present invention provides an internal actuator structure that inserts into and slidably engages the interior of a hollow shaped cylindrical print head. The internal actuator structure extends down out of the print head and is itself pivotally mounted in such a manner to definea fixed axis about which the print head moves. In one embodiment, the fixed axis cooperates with a defined and limited flexible portion of the positioning shaft structure. In another embodiment, the positioning shaft structure is itself of a non-fixed pivotal nature. In both embodiments, the internal actuator structure combines with the associated rotational and axial positioning apparatus to provide composite mutual cooperation between a relatively few number of moving parts.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the present invention reference should be had to the accompanying drawings wherein:

FIG. 1 is a fragmentary perspective view of a serial printer carriage apparatus with a rotatable and axially displaceable print head mounted thereon;

FIG. 2 is a sectional view along line 2'2 of FIG. 1 illustrating the uppermost portion of the print head along with its associated supporting shaft structure;

FIG. 3 is a front sectional view along line 3-3 of FIG. 1 showing the shaft structure extending down from the uppermost portion of the print head through the print head, the drive spline arrangement, the internal actuator, the rotary drive and finally terminating at the outer end thereof;

FIG. 4 is a side elevational view, partly in section, showing the pivoted yoke portion of the internal actuator structure and the flexible coupling portion of the shaft structure;

FIG. 5 is a side elevational view, partly in section, showing an alternative embodiment to that of FIG. 1; and

FIG. 6 is a sectional view along line 66 of FIG. 5 showing the square peripheral engagement between an axially moving shaft and a rotating armature mount.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a print head 10 mounted at the top of a carriage apparatus 12. The carriage apparatus 12 is moveable along guides 14 and 16 by a belt means 18 in the lateral direction as shown. The lateral movement of the carriage apparatus 12 may be accomplished by any means well known in the art and will therefore not be explained in detail. The carriage apparatus 12 is stepped along in the lateral direction so as to laterally position the print head 10 for printing the next character in a row of characters. The print head 10 is also simultaneously rotated and moved axially along an axis 20 so as to position a given raised character 22 on the print head surface for printing. Impact printing is accomplished by moving the print head 10 toward an ink ribbon 24 causing the positioned raised character 22 to be printed on a medium (not shown) in back of the ink ribbon 24.

Turning first to the manner in which the print head 10 is axially positioned, the print head 10 is shown in FIGS. 1-3 as being connected to an axially moveable shaft 26 at a rotatable thrust bearing support structure 27 which will be explained hereinafter. The axially moveable shaft 26 extends down through the print head 10, various other surrounding moving parts, and terminates at a coupling 28. The coupling 28 connects the shaft 26 to a rack 30 which is engagably driven by a pinion 32. The rack 30 and the pinion 32 are maintained in alignment by a guide 34 which in turn is joined to the carriage apparatus 12. The pinion 32 is positioned within the carriage apparatus 12 by a pair of sleeve portions 38 and 40 which extend to either side wall of the carriage apparatus 12 as shown in FIG. 1. The pinion 32 is slidably mounted on a splined shaft 36 that is in turn rotatably driven by a motor not shown). The rack 30 and the pinion 32 are therefore seen to move laterally with the carriage apparatus 12 while simultaneously axially positioning the print head 10 through the coupling 28 and the shaft 26.

Returning now to the rotatable thrust bearing support structure 27 as it is particularly shown in FIG. 2, this structure supports the print head 10 at the top of the axially moveable shaft 26. The rotatable thrust bearing support structure 27 comprises both a lower rotatable bearing 42 and an upper rotatable bearing 44 situated within a housing 46 suitably mounted to the shaft 26. The housing 46 is secured in place by a nut 47 which threadably engages the axially moveable shaft 26. A bearing surface structure 48 is interposed between lower bearing 42 and upper bearing 44. The bearing surface structure 48 is in turn affixed to the inside wall of a long hollow cylinder 50 which extends downwardly around the shaft 26. The long hollow cylinder 50 is free to rotate about the axis 20 and the shaft 26 by virtue of the bearing surface structure 48 freely rotating within the lower and upper bearings 42 and 44 respectively. The long hollow cylinder 50 at the same time moves axially along the axis 20 in response to the axial movement of the shaft 26. This latter motion is'accomplished by virtue of the housing 46 being secured to the shaft 26 by the nut 47.

The long hollow cylinder 50 serves as an inner mounting surface for a hollow cylindrical character drum 52 which is suitably affixed thereto. The hollow cylindrical character drum 52 can be molded from any conventional print head material or it can be made from urethane as disclosed in commonly assigned U. S. Pat. application Ser. No. 69,829, to Cheng I-lua Wang, filed on Sept. 4, 1970. The surface of the character drum 52 contains a matrix arrangement of raised characters, e.g., 22, formed thereon. The preferred matrix arrangement consists of 8 rows and l2 columns. The character drum 52 is so positioned relative to the hollow cylinder that a last row 54 of raised characters is in printing position directly opposite the ink ribbon 24 when the axially moveable shaft 26 is fully extended. A top row 56 of raised character is similarly in printing position directly opposite the ink ribbon 24 when the axially moveable shaft is fully retracted. It can be noted at this time that the above-mentioned matrix arrangement of raised characters that is formed on the hollow character drum 52, and in turn mounted to the long hollow cylinder 50, constitutes what has heretofore been simply referred to as the print head 10.

Turning now to the manner in which the print head 10 is rotatably positioned, a spline guide surface 58 is formed on the inside wall of the long hollow cylinder 50. The spline guide surface 58 engages a drive spline 60for a distance equal to one-half the length of the long hollow cylinder 50. This amount of drive spline engagement provides a stiff and rigid backing for the printing of a raised character within any of the matrix rows. FIG. 1 shows the most extreme case of fully extending the print head 10 in the axial direction while still maintaining drive spline engagement in back of the bottommost row of raised characters 54. This type of drive spline engagement also provides an extremely accurate positioning for any particular row of characters due to the immediate presence of the drive spline behind the subject row.

The drive spline 60 is itself rotated about the axis 20 by virtue of being affixed to a rotatable hollow shaft 62 which begins at the topmost portion of the drive spline and runs down through the center of it. The drive spline 60 terminates at the top of a cylindrical neck 64 while the'hollow shaft 62 continues down through it. The hollow shaft 62 is rotatably supported within the cylindrical neck 64 at cylindrical bearing portions 66 and 68. The same hollow shaft 62 thins down to a non-contact, smaller diameter portion 69 between bearing portions 66 and 68. This type of mounting and shaft geometry provides a rigid support for the rotating hollow shaft structure 62 which is in turn reflected in a stiff drive and an accurate positioning of the print head 10.

The hollow shaft 62 which has been rotatably supported within the cylindrical neck 64 now extends down out of the neck to a flexible coupling 70. As can be seen from FIGS. 1 and 3, the flexible coupling 70 lies within a pivotal yoke 72. The flexible coupling 70 provides a limited and well defined bending point that combines with the pivotal yoke 72 to produce an accurate impact printing stroke by the print head 10. This will be further explained hereinafter when the impact printing feature is discussed. The flexible coupling 70 joins the hollow shaft 62 to a lower hollow shaft 74 which extends down through a motor casing 76 as shown in FIG. 3. An armature'arrangement 82 is affixed to the hollow shaft 74 and is in turn positioned within a surrounding stator arrangement 84. The stator 84 and the armature 82 provide rotational drive to the hollow shaft 74. The shaft 74 in turn rotates the flexible coupling 70, the hollow shaft 62, the drive spline 60,

the spline guide 58 and hence the character drum 52. Stator-armature configurations for the subject rotational drive will be explained hereinafter.

The hollow shaft 74 terminates at a rotational sensor 86 that provides feedback control to the aforementioned stator-armature drive. This marks the bottommost point to which the rotating shaft structure extends. It can be seen from FIGS. 1 and 3 that the axially moveable shaft 26 extends downwardly from this bottommost point and thereafter joins the previously described rack and pinion drive at the coupling 28. It can be furthermore seen from FIG. 3 that the hollow shafts 74 and 62 and the flexible coupling 70 all have an inside diameter significantly larger than the outside diameter of the axially moveable shaft 26. The rack and pinion drive is thus seen to freely move the shaft 26 up and down within the hollow shafting 74, 70 and 62 so as to thereby drive print head through the interconnecting rotatable thrust bearing structure 27. The aforementioned hollow shafting 74, 70 and 62 is at the same time free to rotatably drive the print head through the drive spline 60 and spline guide 58. The positioning of the axial drive beneath the rotating hollow shaft structure together with the axially moveable shaft inserting therethrough thus avoids any complicated interferences between the two drives and allows for each drive to function completely free of the other.

Turning now to specific motor drives which can be used for both the axial and rotational motions. It will first be recalled that in connection with FIG. 1, the axial drive depends from a motor (not shown) that retates the splined shaft 36. It is thus seen that for the FIG. 1 embodiment, both the axial and rotational drives utilize rotary motors. It is furthermore evident that the armature 82, stator 84 configuration which rotates the hollow shaft 74, is of the center-through drive type. A counterpart center through drive is also to be visualized for driving the splined shaft 36.

A type of motor which is very well suited for incrementally moving the respective rotary and axial shafts is a stepping motor configuration. This type of motor configuration is illustratively shown in US Pat. No. 3,374,410 to D. H. Cronquist et al. and essentially consists of a number of coils positioned around the circumference of a stator (i.e., 84 of FIG. 1) which in turn surrounds a permanent magnet armature (i.e., 82 of FIG.

1). The coils are so energized as to position the permanent magnet armature in as many positions as are required. In the-presentinvention, a pair of HS-SO Slo- Syn Precision Steppers (manufactured by Superior Electric) with eight and 12 step positioning capabilities are provided to axially and rotatably position the print head 10. It is thus seen that by employing stepping motors of eight and l2 steps respectively, that any of the characters on the print head 10 may be quickly and accurately positioned for impact printing.

All of the aforementioned positioning structure is itself considered novel'and partially constitutes the subject matter of a commonly assigned U. S. application Ser. No. 94,144 to S. Cahill and C. Pateuk entitled Carriage Apparatus for Serial Printer", filed onDec. l, 1970, now abandoned. The particular impacting apparatus which is now to be described and its cooperation with the aforementioned positioning structure forms the basis of thexclaimed subject matter. of the present invention.

The print head 10 is moved toward the ink ribbon 24 by an internal actuator which inserts into the interior of the print head 10 itself. Some of the internal actuator 100 has already been mentioned including: the pivotal yoke 72, the cylindrical neck 64, and the drive spline 60. It is furthermore to be recalled that the drive spline 60 always inserts far enough into the print head 10 to provide an immediate drive for the given positioned character which is to be impact printed.

Referring to FIG. 3, the pivotal yoke 72 is seen to be suspended by a set of pins 106 and 108 between a pair of upwardly extending carriage mounts 110 and 112 which are themselves part of a cantilevered extension 114 of the carriage apparatus 12. The pins 106 and 108 define a pivotal axis 116 which intersects and passes through the flexible coupling 70 of the previously described hollow shafting. The pivotal yoke 72 rigidly supports the upwardly extending cylindrical neck 64 and contains a set of yoke arms 118 and 120 which extend back from the cylindrical neck 64.

Turning now to FIGS. 1, 3 and 4 and to the structure which implements the pivotal motion of the internal actuator 100. An armature plate 122 is suspended between the yoke arms 118 and 120 and is connected to each arm at points 128 and 130. The armature plate 122 normally defines a gap 132 (as shown in FIG. 4) with respect to an electromagnet 134. When the electromagnet is energized, the armature plate 122 moves toward the electromagnet 134 thus causing the yoke 72 to pivot about the axis 116 as defined by the pins 106 and 108. The pivotal movement of the yoke 72 causes the flexible coupling 70 to bend. about the axis 116 thereby allowing the upper rotating hollow shaft 62 and the print head 10 to move toward the ink ribbon 24 for impact printing. The flexible coupling 70 is seen to constitute a relatively short portion of the total length of hollow shafting which consists of the lower rotating hollow shaft 74, the flexible coupling 70 and the upper rotating hollow shaft 62. Hence it can be seen that the flexible coupling 70 confines the actual shaft bending to a relatively short length. The type of flexible coupling used in the present invention is a Hell-Cal Double Flexing Shaft Coupling 4035D with a length of 0.56 inches and is manufactured by Heli Cal Products Co. of Redondo Beach, Calif. This particular coupling adequately absorbs the resulting concentrated bending moment about axis 1 16 when the desired amount of angular bend is introduced into the shafting to cause the impact printing. While the pivotal motion of the yoke 72 is occurring, the hollow shaft structure 62 is maintained in an essentially undeformed condition by virtue of the cylindrical neck 64 rigidly supporting the hollow shaft 62 at bearing points 66 and 68 respectively. Thus a stiff and rigid straight line configuration is defined between the flexible coupling 70 and the print head 10.

Another approach to impact printing utilizing the subject internal actuation is shown. in FIG. 5. The FIG. 5 structure for impact printing begins with a print head 210 suitably attached at its topmost portion to a flexible shaft 212. The flexible shaft 212 extends down from this'juncture with the print head 10 and eventually attaches to a rigid positioning shaft structure 214. The print head 210 slidably engages a neck portion 216 of an internal actuator 218. The internal actuator 218 is shown as being supported on a cantilevered portion.

220 of a carriage apparatus 222. An armature portion 224 of the internal actuator 218 is normally at a gapped distance 226 from an electromagnet 228. The print head 210 moves toward an ink ribbon 230 and a print medium 232 when the electromagnet 228 is first energized thus attracting the armature 234 and causing both the internal actuator 218 and the print head 210 to pivot about an axis through a mounting pin 234. The flexible shaft 212 is at the same time flexing along its entire length from its attachment point to the rigid positioning shaft structure 214. This type of shaft flexing is characterized by a non-fixed pivoting in comparison to the fixed pivoting of FIGS. 1-3. This non-fixed pivoting does not affect the relative movement of the print heat 210 which is moving with respect to the axis through the mounting pin 234 by virtue of the internal actuator 218.

The print head 210 returns to its normal upright position when the electromagnet 228 is deactivated. The print head 210 is now moved laterally by carriage apparatus 222 along a double set of guides 238 and 240 in much the same manner as previously discussed with respect to FIG. 1. The next character to be impact printed is simultaneously being positioned in both the axial and rotational directions with respect to an axis 242.

The rotational and axial positioning-structure of FIG. 6 is itself considered novel and together with the previously noted positioning structure of FIG. 1 forms the subject matter of the commonly assigned U. S. Pat. application Ser. No. 94,144 to S. Cahill and C. Pateuk entitled Carriage Apparatus for Serial Printer, filed on Dec. 1, 1970, now abandoned. However, the cooperation between the above-mentioned impacting structure and the positioning structure forms part of the present invention.

The positioning shaft structure of FIG. 6 starts with the attachment of the flexible shaft 212 to the rigid positioning shaft 214. The shaft 214 extends down through a rotational motor 244 which is secured to a cantilevered extension 246 of the carriage apparatus 222 by a set of suitable screws 248 and 250. The shaft 214 further extends through a hole 252 in the cantilevered extension 246 and terminates in a rotatable bearing and mount 254. Rotatable bearing and mount 254 allows for the shaft 214 to rotate above an axially moving rack 256 which will be described hereinafter. For the present, it will be seen that the shaft 214 moves up and down within rotational motor 244 by virtue of the axially moving rack 256.

The structure which allows for the axially moving shaft 214 to be simultaneously rotated is as follows. The shaft 214 has a square cross sectional portion 258 as shown in FIG. 6 which extends almost the entire length of the shaft as shown in FIG. 5. This square cross sectional shaft portion 258 slidably engages a complementary square shaft hole 260 which extends the entire length of a rotatable armature mount 262. The rotatable armature mount 262 is rotatably supported at the top and bottom of the motor 244 by a set of bearings 264 and 266. An armature 268 is either wound or affixed to the rotatable armature mount 262. The armature 268 is in turn rotatably driven by a stator 269 which surrounds it.

The rotatably driven armature 268 causes armature mount 262 to rotate within the bearings 264 and 266. The rotating armature mount 262 in turn rotates the square portion 258 by virtue of the square periphery of the shaft portion 258 mating within the square periphcry of the square shaft hole 260. The shaft 214 is thus seen to rotate by virtue of the aforementioned square peripheral engagement while also moving in the axial direction due to the axially moving rack 256.

The axially moving rack 256 rotatably supports the shaft 214 at the rotatable bearing and mount 254. This thus allows the shaft 214 to freely rotate while also moving axially. The rack 256 is driven in the axial direction by a pinion 270 in much the same manner as the rack and pinion system discussed in connection with FIG. 1.

A drive suitable for the aforementioned armature 268 and stator 256 configuration is the rotational stepping motor configuration previously disclosed in connection with FIG. 1. The type of drive inducement to the rotatable armature mount 262 is thus seen to encompass the two previously disclosed armature-stator configurations. It is most important to note that, as a practical matter, any drive arrangement which is to be used should possess the requisite speed and accuracy necessary for a quick and accurate positioning of the print head 210.

While the invention has been particularly shown and described with reference to the preferred embodiments, it will be understood by those skilled in the art that other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. In a serial printer for impact printing a line of characters, a character at a time, onto a print medium, impacting apparatus comprising:

a platform moveably only in spaced character increments in a path parallel to the print line;

a print head aligned along an axis perpendicular to the print line, said print head comprising a hollow shell with a font of characters formed thereon;

positioning means, lying along the axis perpendicular to the print line and attached to said platform, for positioning a given character on said print head, said positioning means comprising; an axially moveable shaft, and axial drive means for driving said axially moveable shaft, and a rotationally moveable shaft, and a rotational drive means for driving said rotationally moveable shaft;

means for pivoting said print head toward the print line, said pivotal means surrounding both said axially moveable shaft and said rotationally moveable shaft and engaging the interior of said print head; and

means for pivotally attaching said pivotal means to said platform so as to define a fixed pivotal axis for said pivotal means; said fixed pivotal axis of said pivotal means intersecting the rotationally moveable shaft, said rotational and axial shafts both extending below said fixed pivotal axis, said axial drive means and rotational drive means being located below said fixed pivotal axis.

'2. The impacting apparatus of claim 1 wherein the pivotal means includes a hollow cylindrical neck extending upwardly into said print head and engaging the interior ofsaid print head.

3. The impacting apparatus of claim 2 wherein the interior of said hollow cylindrical neck rotatably supports said rotationally moveable shaft so' asto provide a rigid, substantially straight line radius of pivot from 9 said fixed pivotal axis of said head.

4. The impacting apparatus of claim 3 wherein said rotationally moveable shaft comprises an upper shaft portion and a lower shaft portion and a flexible coupling fixedly attached to said upper shaft portion and to said lower shaft portion, said flexible coupling being located so as to intersect said pivotal axis of said pivotal means.

5. The impacting apparatus of claim 4 wherein said upper shaft portion and said lower shaft portion of said rotationally moveable shaft comprise hollow shafts and pivotal means to said print said flexible coupling comprises a hollow helical cylinder connected to said upper and lower shaft portions said axially moveable shaft is encompassed by said hollow' shafts and said flexible coupling.

6. The impacting apparatus of claim 5 wherein said means for pivotally attaching said pivotal means to said platform comprises:

a pair of support mounts extending upwardly from said platform, and

a pair of pins each of which passes through a support mount to said pivotal means, said pair of pins being aligned so as to defined said fixed pivotal axis of said pivotal means.

7. The impacting apparatus of claim 1 wherein said rotationally moveable shaft comprises an upper shaft portion and a lower shaft portion and a flexible coupling fixedly attached to said upper shaft portion and to said lower shaft portion, said flexible coupling being located so as to intersect said pivotal axis of said pivotal means.

8. The impacting apparatus of claim 7 wherein said upper shaft portion and said lower shaft portion of said rotationally moveable shaft comprise hollow shafts and said flexible coupling comprises a hollow helical cylinder connected to said upper and lower shaft portions and said axially moveable shaft is encompassed by said hollow shafts and said flexible coupling.

9. The impacting apparatus of claim 7 wherein said pivotal means comprises a hollow cylindrical neck which supportably mounts said upper shaft portion of said rotatable shaft so as to provide a rigid substantially straight line configuration between said flexible coupling and said print head.

10. The apparatus of claim 9 wherein said hollow cylindrical neck extends upwardly into the interior of said print head for a distance at least equal to the axial length of the font of characters formed on the exterior of said print head so that any row of axially positioned characters which is to be impact printed is always rearwardly engaged by said hollow cylindrical neck portion.

11. The impacting apparatus of claim 9 wherein said means for pivotally attaching said pivotal means to said platform comprises:

a pair of support mounts extending upwardly from said platform and 4 a pair of pins each of which passes through a support mount to said pivotal means, said pair of pins being aligned so as to define said fixed pivotal axis of said pivotal means.

12. The impacting apparatus of claim 1 wherein said means for pivotally attaching said pivotal means to said platform comprises:

a pair of support mounts extending upwardly from said platform, and v a pair of pins each of which passes through a support mount and said pivotal means, said pair of pins being aligned so as to define said fixed pivotal axis of said pivotal means. 

1. In a serial printer for impact printing a line of characters, a character at a time, onto a print medium, impacting apparatus comprising: a platform moveably only in spaced character increments in a path parallel to the print line; a print head aligned along an axis perpendicular to the print line, said print head comprising a hollow shell with a font of characters formed thereon; positioning means, lying along the axis perpendicular to the print line and attached to said platform, for positioning a given character on said print head, said positioning means comprising; an axially moveable shaft, and axial drive means for driving said axially moveable shaft, and a rotationally moveable shaft, and a rotational drive means for driving said rotationally moveable shaft; means for pivoting Said print head toward the print line, said pivotal means surrounding both said axially moveable shaft and said rotationally moveable shaft and engaging the interior of said print head; and means for pivotally attaching said pivotal means to said platform so as to define a fixed pivotal axis for said pivotal means; said fixed pivotal axis of said pivotal means intersecting the rotationally moveable shaft, said rotational and axial shafts both extending below said fixed pivotal axis, said axial drive means and rotational drive means being located below said fixed pivotal axis.
 2. The impacting apparatus of claim 1 wherein the pivotal means includes a hollow cylindrical neck extending upwardly into said print head and engaging the interior of said print head.
 3. The impacting apparatus of claim 2 wherein the interior of said hollow cylindrical neck rotatably supports said rotationally moveable shaft so as to provide a rigid, substantially straight line radius of pivot from said fixed pivotal axis of said pivotal means to said print head.
 4. The impacting apparatus of claim 3 wherein said rotationally moveable shaft comprises an upper shaft portion and a lower shaft portion and a flexible coupling fixedly attached to said upper shaft portion and to said lower shaft portion, said flexible coupling being located so as to intersect said pivotal axis of said pivotal means.
 5. The impacting apparatus of claim 4 wherein said upper shaft portion and said lower shaft portion of said rotationally moveable shaft comprise hollow shafts and said flexible coupling comprises a hollow helical cylinder connected to said upper and lower shaft portions said axially moveable shaft is encompassed by said hollow shafts and said flexible coupling.
 6. The impacting apparatus of claim 5 wherein said means for pivotally attaching said pivotal means to said platform comprises: a pair of support mounts extending upwardly from said platform, and a pair of pins each of which passes through a support mount to said pivotal means, said pair of pins being aligned so as to defined said fixed pivotal axis of said pivotal means.
 7. The impacting apparatus of claim 1 wherein said rotationally moveable shaft comprises an upper shaft portion and a lower shaft portion and a flexible coupling fixedly attached to said upper shaft portion and to said lower shaft portion, said flexible coupling being located so as to intersect said pivotal axis of said pivotal means.
 8. The impacting apparatus of claim 7 wherein said upper shaft portion and said lower shaft portion of said rotationally moveable shaft comprise hollow shafts and said flexible coupling comprises a hollow helical cylinder connected to said upper and lower shaft portions and said axially moveable shaft is encompassed by said hollow shafts and said flexible coupling.
 9. The impacting apparatus of claim 7 wherein said pivotal means comprises a hollow cylindrical neck which supportably mounts said upper shaft portion of said rotatable shaft so as to provide a rigid substantially straight line configuration between said flexible coupling and said print head.
 10. The apparatus of claim 9 wherein said hollow cylindrical neck extends upwardly into the interior of said print head for a distance at least equal to the axial length of the font of characters formed on the exterior of said print head so that any row of axially positioned characters which is to be impact printed is always rearwardly engaged by said hollow cylindrical neck portion.
 11. The impacting apparatus of claim 9 wherein said means for pivotally attaching said pivotal means to said platform comprises: a pair of support mounts extending upwardly from said platform and a pair of pins each of which passes through a support mount to said pivotal means, said pair of pins being aligned so as to define said fixed pivotal axis of said pivotal means.
 12. The impacting apparatus of claim 1 wherein said means for pivotally attaching said pivotal means to said pLatform comprises: a pair of support mounts extending upwardly from said platform, and a pair of pins each of which passes through a support mount and said pivotal means, said pair of pins being aligned so as to define said fixed pivotal axis of said pivotal means. 